If asked about the ecology of cartilaginous fish, most people would
probably identify them as rapacious carnivores. Many sharks are predators
on fish, squid, and marine mammals -- although comparatively few are
dangerous to humans. However, other cartilaginous fishes, such as
skates, rays, and chimaeras, live on crustaceans
and molluscs; they lack the daggerlike teeth of predatory sharks, and their
teeth take the form of heavy crushing plates. (Incidentally, the sting
in a stingray's tail is not used for attack or predation; it is purely
for defense.) It may come as a surprise
that several large sharks, like the basking shark featured at the top of
this page, have small teeth and feed on plankton. As they swim in the
open ocean, water is taken in through the mouth and strained through
the gill slits. The largest shark of all,
the whale shark, is such a plankton feeder.